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Background The ectoparasitic mite Varroa destructor is the gravest threat to managed honeybees, and its control relies on a limited number of chemical miticides. Among these, amitraz is widely used because of its strong efficacy against mites and relatively low toxicity to bees. However, increasing resistance to amitraz in Varroa populations threatens its long-term effectiveness. While mutations in the mite’s β2 octopamine receptor are strongly associated with amitraz resistance, additional mechanisms influencing toxicant uptake and efflux are believed to also contribute. ATP-binding cassette (ABC) transporters, including ABCB1/P-glycoproteins, are well-established mediators of xenobiotic efflux and pesticide tolerance across arthropods, making them promising targets for silencing via RNA interference (RNAi) to combat miticide resistance. Methods We cloned a full-length Varroa ABCB1-like transporter ( VdABCB1 ) and synthesized dsRNAs targeting its coding sequence. Adult mites were treated with dsRNA prior to amitraz exposure in laboratory bioassays. Mite survival was analyzed longitudinally, and resistance-associated β2 octopamine receptor genotypes were determined.   Varroa transcriptomic responses to dsRNA were assessed by RNA sequencing. Honeybee safety was evaluated in cage assays following chronic oral dsRNA exposure, including conservative tests co-administered with a known ABC transporter substrate. Results Mites exposed to ABCB1 dsRNA showed greater amitraz-induced mortality than those treated with non-specific dsRNA. This effect was observed across multiple trials and amitraz concentrations. Transcriptomic analyses of mites revealed a significant knockdown of ABCB1-like transcripts following RNAi treatment. Chronic dietary exposure to ABCB1 dsRNA did not impact honeybee survival. Toxicity assays with ABCB1 dsRNA on its own or together with acetamiprid (ABC transporter substrate) as a high-risk interaction control showed minimal adverse effects on bees. Conclusions RNAi suppression of Varroa ABCB1-like transporters increased amitraz mortality in resistant mites, identifying transporter-mediated efflux as a modifiable component of amitraz resistance. These findings demonstrate that targeted disruption of detoxification pathways can enhance miticide efficacy while minimizing off-target effects in bees. RNAi-based synergists therefore represent a selective resistance management strategy that could extend the effective lifespan of amitraz and other miticides relied on by the beekeeping industry. Graphical abstract

Division of labor within a honey bee colony creates a codependence between bees performing different tasks. The most obvious example of this is between the reproductive queen and worker bees. Queen bees lay 1,000 or more eggs a day, while young worker bees tend and feed queens. Young workers and queens can be exposed to pesticides when foragers return to the hive with contaminated resources. Previous research has found negative effects of larval exposure to insect-growth disruptors (IGD) methoxyfenozide and pyriproxyfen, on adult responsiveness to artificial queen pheromone. The present work investigates potential physiological and molecular mechanisms underpinning this behavioral change by examining the development of hypopharyngeal glands and ovaries as well as the expression of genes related to reproduction and worker endocrine signaling in the brain and hypopharyngeal gland tissues. Though hypopharyngeal gland and ovary development were not altered by developmental exposure to IGDs, gene expression differed. Specifically, in the brain tissue, ilp1 was downregulated in bees exposed to pyriproxyfen during development, and Kr-h1 was downregulated in both methoxyfenozide- and pyriproxyfen-exposed bees. In the hypopharyngeal glands, Kr-h1, EcR-A, EcR-B, and E75 were upregulated in honey bees exposed to methoxyfenozide compared to those in the pyriproxyfen or control treatments. Here we discuss these results and their potential implications for the health and performance of honey bee colonies.

Abstract Techniques to monitor honey bee (Apis mellifera) egg production in cages allow researchers to study how different environmental factors contribute to reproduction. However, although the conditions required to facilitate queen egg production in a laboratory setting have been established, limited work has addressed the requirements for stimulating and monitoring worker egg laying. Here, we documented that drone laying workers will lay eggs in Queen Monitoring Cages (QMC), specialized cages designed to facilitate queen egg laying under controlled conditions. Egg production and worker mortality were compared between QMCs containing queens and those containing drone laying workers. High-definition images of the last abdominal segments of living first-instar larvae hatched from worker laid eggs and those putatively laid by queens were qualitatively compared to identify candidate characteristics to determine their sex.

As critical pollinators of agricultural crops, honey bees (Apis mellifera) play a vital role in food production. Therefore, it is imperative to investigate and develop new methods to control Varroa destructor, a devastating parasitic mite of honey bee colonies that weakens bees and spreads deadly diseases that lead to colony loss. Here, we adapted existing methods to investigate the role of ABCB1 transporters in mitigating the toxicity of amitraz, a widely used miticide approved for use in honey bee colonies, demonstrating that a pharmacological inhibitor can synergistically increase amitraz toxicity compared to the equivalent dose of amitraz alone. Evaluations performed on the mites used in one of the described experiments revealed a high proportion of the test subject mites (88.5%) possessed the amitraz resistant genotype, indicating that even in resistant mites, inhibiting ABCB1 transporters can increase amitraz efficacy. This promising finding may be useful in developing powerful synergists that can be used to increase the efficacy of new and existent miticides.